1. Field of the Invention
The present invention relates to an information display device for use in an electronic device such as an electronic watch, and an electronic timepiece including the information display device.
2. Description of the Related Art
For example, as described in Japanese Patent Application Laid-Open (Kokai) Publication No. Heisei 05-87950, an electronic watch has been known in which a display rotor plate is rotatably placed below an hour plate above which pointers move. By the display rotor plate being rotated by an ultrasonic motor, part of a display section such as a calendar display provided on the display rotor plate, for example, a date, is switched corresponding to a display opening of the hour plate.
The ultrasonic motor in the electronic watch described above is structured to include a ring-shaped rotor provided on the lower surface of the display rotor plate, a ring-shaped stator placed below the rotor and made of an elastic body to rotate the rotor, and a plurality of piezoelectric elements provided on the lower surface of the stator to cause the stator to generate oscillatory waves. When the plurality of piezoelectric elements are sequentially energized to be deformed, the deformation causes the stator to generate oscillatory waves along a ring direction of the stator. The oscillatory waves cause the rotor to be rotated.
However, in the electronic watch described above, although the display rotor plate is rotated by the ultrasonic motor to allow part of the display section such as the calendar display, for example, the date, to be switched corresponding to the display opening of the hour plate, if the electronic watch receives an external impact, the display rotor plate may be rotated to shift the position of the part of the display section corresponding to the display opening of the hour plate, for example, the date.
To solve the above-described problem, it has been studied that a load is given by an energizing member such as a spring to the display rotor plate to prevent a positional shift of the display rotor plate due to an impact. In this structure, however, since a load is always given by the energizing member such as the spring to the display rotor plate, a large driving force for rotating the display rotor plate is required, and therefore the display rotor plate is not able to be smoothly rotated.
The present invention provides an information display device and electronic timepiece capable of preventing a positional shift of display such as a date even if an impact is received and smoothly switching the display without requiring a large driving force.